Fight, Flight or Freeze is introduced in Part 1, Chapter 1 of The 7 Skills to impress™.
It is an ancient survival response triggered by perceived danger. When Identity senses a threat, System 1 prepares the body to run away, fight back or freeze. FFF floods the bloodstream with adrenaline and cortisol shutting down rational System 2 thinking.
Managing your state (Part 2, Skill 2) helps you override FFF.